1. Field of the Invention:
The present invention relates to a light scanning apparatus for scanning light emitted from a light source. More particularly, the present invention relates to a light scanning apparatus having a relatively compact structure.
2. Description of the Related Art:
Generally, light scanning apparatuses such as laser scanning units, are applied to image forming apparatuses for printing an image on paper. Examples of image forming apparatuses include copiers, laser printers, and the like. In light scanning apparatuses, light emitted from a light source scans a photosensitive medium to form an electrostatic latent image.
FIG. 1 is a construction diagram of an example of a conventional light scanning apparatus. FIG. 2 illustrates an angle at which a beam of light is incident upon a rotational multi-sided mirror 7.
Referring to FIG. 1, the conventional light scanning apparatus includes a light source 2 formed of a laser diode. A light source controller controls an on/off operation of the light source 2 and a collimating lens 3 to convert divergent laser light emitted from the light source 2 into parallel light or convergent light. The light source controller also controls a cylinder lens 5 for making laser light which passes through the collimating lens 3 to have a bar-shaped cross-section. Additionally, the light source controller controls the rotational multi-sided mirror 7 for deflecting laser light, an f-θ lens 9 disposed between the rotational multi-sided mirror 7 and a to-be-scanned surface 20, a reflection mirror 11 reflecting laser light for use in synchronous signal detection, a synchronous signal detection lens 13 collecting the laser light reflected by the reflection mirror 11, and a photodetector 15 to receive laser light for use in synchronous signal detection. The light source controller is comprised of a semiconductor device installed on a circuit board 1 and a control circuit formed in a predetermined pattern. The light source 2 and the photodetector 15 are generally installed on the circuit board 1 in order to minimize the size of the light scanning apparatus and to reduce manufacturing costs.
Referring to FIG. 2, laser light beam A1 is incident upon the rotational multi-sided mirror 7 at an angle θ1 with a normal line N1 of a mirror side 7a. The rotational multi-sided mirror 7 is hexagonal. A length L1 of each side of the rotational multi-sided mirror 7 is proportional to the incidence angle θ1. Thus, as the incidence angle θ1 increases, the length L1 of each side of the rotational multi-sided mirror 7 increases. Consequently, the rotational multi-sided mirror 7 is enlarged. Enlarging the rotational multi-sided mirror 7 leads to increased costs for manufacturing the light scanning apparatus. Also, noise generated due to rotation of the rotational multi-sided mirror 7 is increased.
As shown in FIG. 1, in order to solve the above-described problems, the light source 2 and the circuit board 1 may be disposed so that a light beam is incident upon the rotational multi-sided mirror 7 at an angle to the to-be-scanned surface 20 instead of being parallel thereto. However, in this case, the photodetector 15 is rendered aslant. Consequently, the laser light used in synchronous signal detection is incident aslant upon a light receiving surface of the photodetector 15. Consequently, the reliability of synchronous signal detection degrades.
Accordingly, there is a need for a light scanning apparatus in which light is incident upon a side of a rotational multi-sided mirror at an angle smaller than that in a conventional light scanning apparatus.